Two years ago it failed the same item. I passed it with an OEM O2
sensor. Could the O2 sensor go bad in two years? Is there a way to
check the O2 sensor? I did more than replacing the O2 sensor two years
ago. I put in a complete new exhaust from the header on.

"yaofeng" <yaofengchen@gmail.com> wrote:
>Going in I knew if it fails the New Jersey State inspections, it will
>be emissions and it would be high NOx. Indeed it did.
>
>My 93 940 wagon passed all mechanical inspections and failed emieeions.
> The CO, HC numbers are below spec. NOx is at 1,226, above the 937
>limit.
>
>Two years ago it failed the same item. I passed it with an OEM O2
>sensor. Could the O2 sensor go bad in two years? Is there a way to
>check the O2 sensor? I did more than replacing the O2 sensor two years
>ago. I put in a complete new exhaust from the header on.

1981-86
Check the following:
O2 sensor (The signal from the O2 Sensor provides a wealth of
information on how the vehicle is running.)
EGR valve and EGR hose
Ignition timing and system (advanced timing and ignition components
are some of the most common problems).
Vacuum lines (deterioration of vacuum lines, inlet manifold seals, and
become more prevalent causes with age).
Catalytic converter
Primary feedback sensor failure including, oxygen sensor, MAP/MAF,
TPS, RPM, and CTS sensors.

1987-95
Check the following:
Use OBD, if available
O2 sensor
EGR valve and EGR hose
Ignition timing and system (advanced timing and ignition components
are some of the most common problems)
Primary feedback sensor failure including, oxygen sensor, MAP/MAF,
TPS, RPM, and CTS sensors
Vacuum lines
Catalytic converter
_____________________________________________

Oxides Of Nitrogen (nox)
Nitrogen makes up about 78% of the air we breathe. Though normally
inert and not directly involved in the combustion process, combustion
temperatures above 2500 degrees F cause nitrogen and oxygen to combine
and form various compounds called "oxides of nitrogen," which is
abbreviated NOX. This mostly occurs when the engine is under load and
the throttle is open wide.

NOX is a nasty pollutant both directly and indirectly. In
concentrations as small as a few parts per million, it can cause eye,
nose and lung irritations, headaches and irritability. Higher
concentrations can cause bronchitis and aggravate other lung
disorders. Once in the atmosphere, it reacts with oxygen to form ozone
(which is also toxic to breathe) and smog.

To reduce the formation of NOX, Exhaust Gas Recirculation (EGR) is
used. By recirculating a small amount of exhaust gas back into the
intake manifold to dilute the air/fuel mixture, EGR has a "cooling"
effect on combustion, thus keeping temperatures below the NOX
formation threshold.

On 1981 and later engines with computerized engine controls, a special
"three-way" catalytic converter is used to reduce NOX in the exhaust.
The first chamber of the converter contains a special "reduction"
catalyst that breaks NOX down into oxygen and nitrogen. The second
chamber contains the "oxidation" catalyst that reburns CO and HC.

High NOX emissions are almost always due to a defective EGR valve (or
some component that controls the operation of the EGR valve). A
related symptom that usually occurs when EGR is lost is spark knock
(detonation) during acceleration.
--------------------------------------------
FROM:http://www.wivip.com/fs_motorist.htm...clefailed.html

Nitrogen Oxides (NOx)
Nitrogen Oxides is a group of highly reactive gases that contain
nitrogen and oxygen in varying amounts. Many of the nitrogen oxides
are colorless and odorless. One such gas, nitrogen dioxide (NO2) can
often be seen combined with airborne particles as a reddish-brown
layer over many urban areas. Nitrogen oxides are formed when the
oxygen and nitrogen in the air react with each other during
combustion. The formation of nitrogen oxides is favored by high
temperatures and excess oxygen (more than is needed to burn the fuel).
The primary sources of nitrogen oxides are motor vehicles, electric
utilities, and other industrial, commercial, and residential sources
that burn fuels.

Nitrogen Oxides in vehicles are caused by excessive combustion chamber
temperatures. Some of the common causes of high NOx emissions are
problems with the vehicle's Exhaust Gas Recirculation System (EGR),
improper ignition timing, lean air/fuel mixture and malfunctions in
systems that control engine temperature, such as the thermostat and
cooling fan, and vacuum leaks. Due to the complexity of the internal
combustion engine, other components may cause high NOx as well.
_____________________________________________

Oxides of Nitrogen (NOx) emissions occur when fuels are burned at high
temperature. Some of the nitrogen (N2) in the air combines with some
of the oxygen (O2) in the air to form nitric oxide (NO). In an engine,
some of the NO undergoes additional reactions and turns into nitrogen
dioxide (NO2). The emissions of NO and NO2 are collectively referred
to as NOx. In addition to contributing to the formation of ozone, NOx
emissions also lead to a build up of nitrogen dioxide levels in the
atmosphere, which are known to increase the risk of respiratory
disease in children.

Exhaust Gas Recirculation (EGR) System Testing

The purpose of the EGR system is to recirculate a small amount of
burned exhaust gases back into the engine under certain operating
conditions. This lowers the temperature of combustion and, in doing
so, reduces the formation of Oxides of Nitrogen (NOx).

It is easy to see then that the EGR is a device that primarily affects
NOx emissions. However, certain EGR defects can also cause excessive
HC emissions.

The first thing the technician should check on every EGR system is the
exhaust passage. Adequate exhaust gas must be available to the EGR
valve for the maximum flow (highest load) conditions. In most cases
they can test this by manually opening the valve at idle and stalling
the engine. If the engine does not stall, it should drop by at least
300 rpm. Otherwise, there is probably a restriction in the exhaust
passage or pipe.

To test the EGR valve and its related components, the technician must
monitor the valve to see that it is opening and closing the proper
amount under the proper conditions. In some cases this will involve
removal of the valve.

Many different controls are used in various types of vehicles to
control and monitor the operation of the EGR valve. In many cases, the
technician will need to refer to the manufacturer's recommended
procedure to troubleshoot the EGR controls. However, some general
procedures the technician should apply are shown below.

* Pressure feedback sensors and modulators should be checked for
any blockage or restriction in the backpressure sensing tube.
* Pressure feedback sensors should be checked electrically for
proper reference voltage, ground, and signal return to the PCM.
* EGR valve position sensors should be checked electrically for
proper reference voltage, ground, and signal return to the PCM.
* EGR temperature sensors should be checked for proper reference
voltage and ground. Temp sensors should also be checked for correct
resistance using the manufacturer's specifications.
* EGR vacuum control solenoids should be checked for the correct
pulsed ground and voltage. Solenoids should also be checked for
correct resistance using the manufacturer's specifications.
* Venturi vacuum amplifiers should be checked for correct vacuum
input and output using the manufacturer's recommended procedures and
specifications.
* Thermostatic vacuum switches should be checked to ensure they
switch properly and allow vacuum to pass through only when the engine
is warm (or vice-versa for some switches). Also, remember that a low
coolant level may prevent correct operation of any temperature sensor
or switch.
* All associated vacuum hoses and fittings should be checked for
cracks, leakage, and secure connections.
* The exhaust system should be checked for modifications that may
be adversely affecting exhaust backpressure and the control of the
EGR.

Possible Causes of High Oxides of Nitrogen (NOx) Emissions

In order to pinpoint the cause of excessive NOx emissions, the
following systems (if applicable) and possible defects will need to be
checked, usually in this order:
Over-Advanced Ignition Timing

Older vehicles have ignition timing systems that are adjustable and,
unfortunately, anything that is adjustable is also mal-adjustable.

Fortunately, ignition timing is usually quick and easy to check. For
more details, see Ignition System Testing.
Inadequate Exhaust Gas Recirculation (EGR) Flow

Operation of the Exhaust Gas Recirculation (EGR) system should be
checked completely. To do this there are three areas that the
technician must check:

* the EGR valve
* the EGR exhaust passage(s)
* the EGR control system

For more information on these procedures see Exhaust Gas Recirculation
(EGR) System Testing.
Lean Air-Fuel Ratio

The technician should check to ensure that there is not an excessively
lean mixture being burned. Depending on the vehicle, its fuel system,
and its emissions control systems, this may involve simply looking at
the VIR, measuring engine-out emission levels, and O2 sensor testing.

Your technician should test the catalyst by performing a converter
efficiency test (see Catalytic Converter Testing). Note that this only
applies if the vehicle is equipped with a three-way catalytic
converter (some 1980-87 vehicles and all 1988 and newer vehicles have
three-way catalytic converters).
Combustion Chamber Deposits

If the above possibilities have been conclusively checked and no
problems found, it is reasonable to conclude that combustion chamber
deposits are contributing to excessive NOx emissions.
______________________________________________

In article <1130437279.646366.106380@g14g2000cwa.googlegroups.com>,yaofengchen@gmail.com says...
> Going in I knew if it fails the New Jersey State inspections, it will
> be emissions and it would be high NOx. Indeed it did.
>
> My 93 940 wagon passed all mechanical inspections and failed emieeions.
> The CO, HC numbers are below spec. NOx is at 1,226, above the 937
> limit.
>
> Two years ago it failed the same item. I passed it with an OEM O2
> sensor. Could the O2 sensor go bad in two years? Is there a way to
> check the O2 sensor? I did more than replacing the O2 sensor two years
> ago. I put in a complete new exhaust from the header on.
>
>
In a nutshell there are very few reasons for high NOx:

Too much ignition advance, which on your car you can do nothing about.

Too much carbon on the tops of the pistons that raises the compression.
Normally doesn't occur on Volvos later than about 1975, but if you want
to try a motorvac with BG chemicals or try a SeaFoam treatment go ahead
it won't hurt, especially if you have high mileage at this point.

Too much carbon on the backs of the intake valves forcing a lean
condition that should be accomodated by the fuel trims in the injection
control unit or a bad O2 sensor that would produce the same thing. If
you were outside the correctable range of the computer the check engine
light would display. A MotorVac will also address this issue.

That leaves the catalytic converter as the usual culprit. If when the
exhaust was replaced you used an aftermarket cheapie converter it may
well have failed by now. Check the docu,entation for the replacement
unit and if it isn't declared suitable for replacement in California
then when new it will barely pass NOx in the states that use the
treadmill (dyno) test for emissions.

Bob.
--
The goal when driving is to miss the maximum number of objects.

User wrote:
> In article <1130437279.646366.106380@g14g2000cwa.googlegroups.com>,
> yaofengchen@gmail.com says...
> > Going in I knew if it fails the New Jersey State inspections, it will
> > be emissions and it would be high NOx. Indeed it did.
> >
> > My 93 940 wagon passed all mechanical inspections and failed emieeions.
> > The CO, HC numbers are below spec. NOx is at 1,226, above the 937
> > limit.
> >
> > Two years ago it failed the same item. I passed it with an OEM O2
> > sensor. Could the O2 sensor go bad in two years? Is there a way to
> > check the O2 sensor? I did more than replacing the O2 sensor two years
> > ago. I put in a complete new exhaust from the header on.
> >
> >
> In a nutshell there are very few reasons for high NOx:
>
> Too much ignition advance, which on your car you can do nothing about.
>
> Too much carbon on the tops of the pistons that raises the compression.
> Normally doesn't occur on Volvos later than about 1975, but if you want
> to try a motorvac with BG chemicals or try a SeaFoam treatment go ahead
> it won't hurt, especially if you have high mileage at this point.
>
> Too much carbon on the backs of the intake valves forcing a lean
> condition that should be accomodated by the fuel trims in the injection
> control unit or a bad O2 sensor that would produce the same thing. If
> you were outside the correctable range of the computer the check engine
> light would display. A MotorVac will also address this issue.
>
> That leaves the catalytic converter as the usual culprit. If when the
> exhaust was replaced you used an aftermarket cheapie converter it may
> well have failed by now. Check the docu,entation for the replacement
> unit and if it isn't declared suitable for replacement in California
> then when new it will barely pass NOx in the states that use the
> treadmill (dyno) test for emissions.
>
> Bob.
> --
> The goal when driving is to miss the maximum number of objects.

I am somewhat skeptical of the bad cat in two years having had a
similar experience with one of my SAAB 9k's. Following someone's
advice to replace the cat after failing NOx, the new cat didn't lower
the NOx at all. In the end it was simply the spark plugs have a gaps
too wide.

But I am interested in the motorvac. What is it. Could you provide
more details?

In article <1130504614.383814.149330@g43g2000cwa.googlegroups.com>,yaofengchen@gmail.com says...
>
> User wrote:
> > In article <1130437279.646366.106380@g14g2000cwa.googlegroups.com>,
> > yaofengchen@gmail.com says...
> > > Going in I knew if it fails the New Jersey State inspections, it will
> > > be emissions and it would be high NOx. Indeed it did.
> > >
> > > My 93 940 wagon passed all mechanical inspections and failed emieeions.
> > > The CO, HC numbers are below spec. NOx is at 1,226, above the 937
> > > limit.
> > >
> > > Two years ago it failed the same item. I passed it with an OEM O2
> > > sensor. Could the O2 sensor go bad in two years? Is there a way to
> > > check the O2 sensor? I did more than replacing the O2 sensor two years
> > > ago. I put in a complete new exhaust from the header on.
> > >
> > >
> > In a nutshell there are very few reasons for high NOx:
> >
> > Too much ignition advance, which on your car you can do nothing about.
> >
> > Too much carbon on the tops of the pistons that raises the compression.
> > Normally doesn't occur on Volvos later than about 1975, but if you want
> > to try a motorvac with BG chemicals or try a SeaFoam treatment go ahead
> > it won't hurt, especially if you have high mileage at this point.
> >
> > Too much carbon on the backs of the intake valves forcing a lean
> > condition that should be accomodated by the fuel trims in the injection
> > control unit or a bad O2 sensor that would produce the same thing. If
> > you were outside the correctable range of the computer the check engine
> > light would display. A MotorVac will also address this issue.
> >
> > That leaves the catalytic converter as the usual culprit. If when the
> > exhaust was replaced you used an aftermarket cheapie converter it may
> > well have failed by now. Check the docu,entation for the replacement
> > unit and if it isn't declared suitable for replacement in California
> > then when new it will barely pass NOx in the states that use the
> > treadmill (dyno) test for emissions.
> >
> > Bob.
> > --
> > The goal when driving is to miss the maximum number of objects.
>
> I am somewhat skeptical of the bad cat in two years having had a
> similar experience with one of my SAAB 9k's. Following someone's
> advice to replace the cat after failing NOx, the new cat didn't lower
> the NOx at all. In the end it was simply the spark plugs have a gaps
> too wide.
>
> But I am interested in the motorvac. What is it. Could you provide
MotorVac is

You disconnect the fuel lines and fill the machine from the tank, add
the proper detergent to the fuel, bypass the fuel lines so that the fuel
pump recirculates fuel directly back to the tank, let the machine
circulate the detergent-fuel micture in the the fuel rail for 20 minutes
or so. Then you Start the motor and run the detergent fuel mixture
through the injectors and engine for another 20-30 minutes. Disconnect
the machine, reconnect the fuel lines to the motor and take the car for
a spirited test drive. If you remeasure the tail pipe emissions with a
five-gas analyzer you will see a significant reduction in HC and NOx,
with perhaps a slight increase in CO. This is more apparent if you
measure at the test port ahead of the converter.

I've replaced converters on 740's with the cheap Bosal/Walker units and
have them barely pass after replacement and then have them pass with
flying colors two years later.

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